MySQL many-to-many SELECT query

Question

I have a Product table, a Tags table and a table that links them together, ProductTags .

Product

ID

ProductTags

ProductID
TagID

Tags

ID

I want to query the ProductTags table for all ProductIDs that have both TagID 1 and 2. How would I do this?

SELECT *
From ProductTags
Where TagID = 1
    AND TagID = 2

This obviously won't work... can't quite get my head round how to do it!

Any help much appreciated!

Answer 1

This is a "set-within-sets" query and I like to solve these using group by and having . Here is one method:

SELECT ProductId
FROM ProductTags
WHERE TagID IN (1, 2)
GROUP BY ProductId
HAVING COUNT(DISTINCT TagId) = 2;

Answer 2

You need to use group by and having for this case

select 
p.id
from product p
join producttags pt on pt.ProductID = p.id
join tags t on t.id = pt.tagid
where pt.tagid in (1,2)
group by p.id
having count(*) = 2 

Answer 3

尝试两次加入ProductTags表。

SELECT t3 From ProductTags t1 join  ProductTags t2 on t1.productId=t2.productId join Product t3 Where t1.TagID = 1 AND t2.TagID = 2

Answer 4

Try This:

SELECT * From ProductTags
Where TagID = 1 OR TagID = 2